The Palestinian Authority and Christian leaders have signed an accord to repair the Church of the Nativity in Bethlehem, on the traditional site of Jesus's birth.

The $US1 million project, to be carried out by an international consortium supervised by Italian renovations expert Remigio Rossi, will fix leaks in the roof that could otherwise threaten the interior of the building.

The funding will come from the Palestinian Authority, and prime minister Salam Fayyad was on hand for the signing ceremony.

"This renovation is the first of its kind in the modern history of Palestine and the first of this size to be carried out on the church," he said.

It will be the first such maintenance project to be carried out on the roof in 200 years, according to the Catholic custodian of the church, which is shared by the Catholic, Greek Orthodox and Armenian Orthodox denominations.

"This is the beginning of a new era of living together in Bethlehem. This basilica had become the symbol of our incapacity to speak to each other," said Father Pierbattista Pizzaballa for the Roman Catholics.

"I hope that it will become, on the contrary, the new space where the churches will be able to demonstrate their capacity to collaborate," he said.

The first phase of the project is due to be completed in 150 days, according to Ziad al-Bandak, who heads the presidential commission supervising the work.

The UN Educational, Scientific and Cultural Association (UNESCO) has said the leaks in the roof threaten wall and floor mosaics in the building, which dates back to the fourth century.

The massive church, built on the site where Christians believe Mary gave birth to Jesus, attracts hundreds of thousands of pilgrims each year and is the main tourist attraction in the Palestinian territories.

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